Design and Real Fluid Modelling of Micro-Channel Recuperators for a Nominal 100 MW Class Recuperated Recompression Brayton Cycle Using Supercritical Carbon Dioxide

Abstract

The goal of this study is to design and assess the effectiveness of a micro-channel recuperator using supercritical carbon dioxide as a working fluid. A one-dimensional thermal analysis is performed for a micro-channel recuperator suitable for a Brayton cycle with a nominal 100 MW class turbomachine. The impact of supercritical carbon dioxide properties near the critical point on the thermal performance of the recuperator is studied in detail. The cycle parameters are first obtained from an overall cycle analysis. Two adjacent flow passages with square cross-section in counter-flow configuration are considered for this analysis along with appropriate symmetry. The high pressure of SCO2 is also addressed and the structural stresses on the micro-channel walls are analyzed. Only the axial temperature variations in the hot stream and the cold stream are considered in the one-dimensional analysis. Each channel is discretized in the axial direction. Axial conduction through the wall is included in the energy balance. Of particular interest in this analysis is the variation of transport properties of the CO2 working fluid as thermodynamic conditions approach the critical point. These property variations are provided to the computer code through the REFPROP database. Over the length of the heat exchanger local changes in Reynolds number, Nusselt number, and heat transfer coefficient are charted. From the results of the heat transfer calculations, the log mean temperature difference and heat exchange effectiveness of the heat exchanger is calculated. Using the code to produce multiple results, the optimum heat exchanger design is found. Recommendations on the manufacturing method of a micro-channel recuperator are made.

Design and modeling of printed - circuit heat exchangers and centrifugal compressors for supercritical carbon dioxide

“…Baik et al (2015) [53] investigated experimentally the thermal-hydraulic performance of a PCHE used as precooler in a supercritical CO2 Brayton cycle, and the results were compared with the performance of a conventional shell-andtube heat exchanger, resulting in a lower pressure drop for the PCHE. Schmitt et al [54] conducted a numerical design study of a PCHE for a 100 MW s-CO2 Brayton cycle, focusing on the Reynolds number, the Nusselt number and the fluid temperature along the high and low temperature recuperator and resulting in an overall heat transfer coefficient of 850 W/(m 2 K) and 1097 W/(m 2 K) respectively. Khan et al (2015) [55] studied numerically wavy (zigzag) channels using threedimensional numerical model(CFD), resulting in thermal-hydraulic characteristics and incorporating the incline angles in this study in order to investigate the secondary flow regimes.…”

“…As a result, the length of the heat exchanger is discretized into a number of elements in series, where the heat is transferred between the hot and cold streams in each element. The heat transfer is considered that takes place in one dimension (x-direction) as presented in Figure 4.1, and consists the most common approach of PCHE study, in order to calculate the effectiveness and other pertaining parameters of every element [54,60,62,95]. There are two methods to define the heat exchanger size.…”